PROJECT SUMMARY ? ABSTRACT Drug addiction is an insidious mental health problem that has few effective therapies. This proposal is a collaborative effort between the PI (Dr. Hnasko) and the Sanford Burnham Prebys Medical Discovery Institute (SBP). SBP has recently identified ML314 and small molecule analogs that act at the Neurotensin receptor type 1 (NtsR1) as biased positive allosteric modulators (PAM). Neurotensin (NT) agonists have long been sought as potential treatments for drug addiction or other psychiatric illness due to the close association of this peptide with the midbrain dopamine system. Indeed, dopamine neurons express both the peptide and the receptor; and NT has been shown to act as an important modulator of dopamine signaling across multiple systems. A promising ML314 derivative NtsR1 PAM developed by SBP has shown excellent blood brain barrier penetration and ADME/Pk/Tox properties that support minimal efficacious doses across multiple models of 10 mg/kg. This compound has also shown promise in normalizing behaviors in pre-clinical models of schizophrenia and addiction. But despite substantial molecular pharmacology characterization using cell-based assays in vitro, and the promising pharmacokinetic and behavioral data described above, very little is understood about how the NtsR1 PAMs developed by SBP influence physiologically intact neural circuits. Understanding this is crucial for directing these promising drugs toward appropriate clinical application/s, developing appropriate biomarkers of clinical efficacy, and developing further refined analogs. Because dopamine is a central player in the manifestations of numerous forms of mental illness, particularly drug addiction; we propose to use mouse models and brain slice preparations to characterize the effects of NtsR1 PAMs on dopamine neuron excitability and dopamine neuron release properties using electrophysiological, electrochemical, and optogenetic approaches. We will also assess how NtsR1 PAMs modulate dopamine neuron plasticity and behavior in animal models of drug addiction/dependence. These experiments are thus aimed directly at accelerating the path of an already highly developed and very promising ligand forward toward the clinical treatment of mental illness, with an emphasis on drug addiction.